HDU Plaque Fail When Inset in Stone

[HandyManBill]

HDU is guaranteed not to warp.

I would contact the manufacturer and get some input from them.
Duna board is good stuff. Having to back that stuff when it is guaranteed not to warp seems to be an unreasonable expense. A closed cell product repels moisture and has no reason to curl or act like wood. It would be time to find a real expert to get an answer.

There are posts around different sites that show HDU failing like this. One common detail is that the panel was not painted the same on all the sides. To me that makes more sense as an explanation than anything else.

Thanks Techman, I just emailed the manufacturer with a link to this forum and this thread.
With regard to the "painting"...it was "coated the same on all sides" with polyester resin that has powdered iron in the mix. I do understand that if you only coat one side or paint one side you are probably going to get a warp or cupping with the concave side on the face. What I am experimenting with is applying a layer of fiberglass cloth 4-6 oz and then finish the front...guess I will see.

Thanks,
Bill